Well, need is the mother of innovation, as they say. In reality, most people are content with what the world looks like now. Military is the only place that needs to be one step ahead of "the enemy", whoever they are. Other dangerous fields also contribute, but they mostly fight against nature, from which we know what to expect. In military, there's constant competition between countries, which drives the progress. When this competition vanes, so does the innovation.
WWII brought us from prop-driven monoplanes to jets. Cold War brought us from alcohol-powered glorified fireworks to 100m tall rockets that gave us the Moon landing. And now what? Cold War is done, and we haven't left LEO since then. We could've had nuclear engines and Mars spacecraft by now, but we don't. When there's no "evolutionary pressure" for designs, we tend to settle for "good enough, let's not fix what's not broken" approach. Military, especially when there's a war or arms race going on, generally provides this pressure. On the other hand, civilian world advances slower, because even with the competition between two companies, it focuses on improving existing things, not inventing new ones.